It is recommended that glove boxes and the like facilities which receive radioactive or toxic materials are provided with ventilation systems which can provide an emergency extract capability in the event of a breach of the containment, for example in the case of the loss or rupture of a glove. It is known to employ vortex amplifiers for this purpose and in situations which involve dry and dusty conditions within the glove box to utilize two extract flow lines, namely a normal and an emergency extract, between the box and an extract source, usually asuction pump. Each line can include a vortex amplifier and a filter. Alternatively, the normal extract line can be a direct connection containing a valve with the emergency extract line having a vortex amplifier. Under normal operational conditions the vortex amplifier in the emergency extract operates in a reverse purge mode to prevent blockage of its associated filter and thereby maintain the emergency extract capability. This reverse flow into the glove box which is obtained from atmospheric air admitted at the control port or ports of the vortex amplifier can result in difficulties when it is required to maintain an inert gas atmosphere within the glove box.